Archit. a molding of a cornice, whose profile is a line partly convex and partly concave
See cyma in American Heritage Dictionary 4
cy·ma
noun
Either of two moldings, cyma recta or cyma reversa, having an undulating or S-shaped profile, used especially in classical architecture. Also called cymatium.
Origin: New Latin cȳma, from Greek kūma, wave, cyma, from kuein, to swell; see keuə- in Indo-European roots.